New Information on How Cutting the Nerves in the Wrist Affects MotionWhen you move your wrist up and down and back and forth, you are able to sense just how much movement is occurring. The sense of joint position and movement makes up what we call proprioception and kinesthesia.
For a long time, we thought the information about proprioception and kinesthesia that was sent to the brain via the sensory nerves all came from the joint itself. But over the years with scientific investigation, researchers have been able to show that there are kinesthetic and proprioceptive sensory receptors located in many places in the joint and soft tissues.
Knowing that transmission of information about joint proprioception can come from the ligaments, tendons, muscles, joint surface, and skin is important. Surgery cutting into any of these structures can destroy them. Then the joint's ability to detect motion and position could potentially be altered.
In this study, researchers from the Division of Orthopaedic Research at the Mayo Clinic in Rochester, Minnesota took a closer look at wrist kinesthesia. They tested and measured the potential effect of denervating two nerves in the wrist on active and passive wrist motion. In the real surgical procedure, the nerves causing chronic pain would be cut. The purpose of the procedure is to eliminate wrist pain.
In this study, the subjects' wrists were injected with a specific solution. The idea was to mimic denervation but without actually killing or permanently altering the sensory nerves responsible for transmitting information.
Two groups of normal adults between the ages of 20 and 54 were included in the study. A total of 80 people participated. One group received a real anesthetic to block the anterior and posterior interosseous nerves. The second (control) group received an injection of a saline (salt) solution to the same nerves.
After the injection, they measured the accuracy (or alternately, the error) in active and passive wrist motion. They did this by placing the wrist in one position and asking the patients to (as accurately as possible) reposition the joint to match the first position. Positions used included 10, 20, and 30-degrees of both wrist flexion and extension. The difference between the actual position and the place the volunteer moved the wrist to was calculated.
Two trials were completed (performed randomly) in each position with a rest of 30 seconds between. The wrist was fully relaxed between trials. They found there were no differences between the groups in ability to reproduce the test position. This indicates that even with nerve anesthetization (mimicking denervation), it is possible to accurately detect active and passive wrist motion. In other words, kinesthetic sense is not impaired or altered by blocking the nerves.
The authors suggest these results infer that effective partial denervation procedures are safe. The accessory nerves are still able to transmit important information about propriocetpion even with the sensory nerves blocked.
This finding provides further evidence that joints aren't the only ones involved in producing proprioceptive messages. In fact, if anything, sensory receptors in the articular surface of joints don't send messages until the joint is at its extreme ends of motion (full flexion or full extension).
The sensory receptors in the joint surfaces appear to have more of a protective role. There may be reflexes at the ligament-muscle interface that help regulate muscle contraction and regulate load on the joints. Evidence to support this idea point to the role of ligaments in joint stability AND motion.
The results of this study suggest that partial denervation of sensory nerves in the wrist is a safe procedure. But more study is needed before this conclusion can be completely proven. Proprioception (including kinesthetic sense) is a complex phenomenon.
This study just looked at one aspect of proprioception. Similar studies are needed to assess the effect of denervation on other components of proprioception and kinesthesia. For example, sensation of force and heaviness during muscle contraction, timing of motor control, and
Andre Gay, MD, et al. Effect of Partial Wrist Denervation on Wrist Kinesthesia: Wrist Denervation Does Not Impair Proprioception. In The Journal of Hand Surgery. November 2011. Vol. 36A. No. 11. Pp. 1174-1179.
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